Metal Fatigue

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sertem90

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Hey Guys !!

Another thing that is very interesting to me. Metal fatigue !!

I have one thing in my mind about bracings cantilever from down to up or up to down.

I do braces to cantilever most of the time down to up at 45 degree. But i had conversation with one layher training manager and he told me that i should consider metal fatigue if i put brace down to up. And said try to put always up to down.

Is that really matter?

Anybody faced that issue and have you ever heard any accident because of metal fatigue?

Professionals im waiting your response !! :) :idea:
 
If anything it's stronger in compression or 'down to up' to use your vernacular than in tension.
How many lifts are going on this cantilever? Wouldn't this 'metal fatigue' manifest itself in other parts of the scaffold such as standards and ledgers or is it just pick ups?
 
A tube in tension will always be better than a tube in compression, in all my years at this game I have yet to see a stretched tube but plenty of bent ones. I would tell your layer guy that components would fail before a tube in tension.
 
The safe axial tensile load for type 4 tube is 79.1 kN. SWL of a class A coupler is 6.1 kN so you need ~12 No supplementary couplers. maybe more if you count that the supp. coupler is only doing 50% of the work/coupler. Pull-back braces put more work onto the ties though.
 
Metal fatigue would never occur on a steel scaffold tube if the loadings are within the safe working limit of the steel. As Nick says a steel tube is far stronger in tension than compression but the coupler is the limiting value for most scaffold scenarios. The load in the tie would be the same for either tension or compression braces, providing the angle is the same. The choice of whether to use tension or compression braces (or rakers) is often more to do with construction methods chosen by the designer or scaffolder than the capacity of the tube.
 
and if your still not sure rope up some old school 21" ladder beams and use them ,
but make sure you double them up as this fatigue is quite catchy
 
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